The invention disclosed herein pertains to a scroll sign module comprised of two rolls that are mounted between the sides of a frame in spaced apart relationship for rotating bidirectionally about parallel axes to wind an information bearing web onto one roll as the web unwinds from the other roll.
Roll sign modules have various applications including, but not limited to displaying prices of goods or services or other information that must be readable from a substantial distance. Displaying the price of vehicle fuel is a typical use of such modules. In this use, several modules are arranged in juxtaposition, to compose the price of fuel, and are mounted on a pole at a great height adjacent a highway for being visualized by vehicle drivers at a great distance from the sign installation site.
Several types of scroll sign modules are known. A typical module has an electric motor operatively coupled in driving relation with two spaced apart parallel rolls by means of a suitable mechanism including gears, chains, sprockets, toothed belts and pulleys. Typically, at least one roll in a parallel pair is coupled to a driving source inelastically for positive driving and the other roll in a pair is a so-called tension roll that is driven rotationally through the agency of an elastic device such as a helical or spiral spring. The spring that is coupled to a driven axle and the tension roll provides for maintaining a substantially constant tension in that part of the indicia displaying web which is stretched between the two rolls even though the overall diameter of the rolls plus the web wrapped on them increases on one roll and decreases on the other roll as the web is wound and unwound, respectively.
U.S. Pat. No. 734,982, which was granted to Smith on Jul. 28, 1903, discloses a scroll module wherein a tension roll is journaled for rotation on a rotationally driven shaft. A spiral spring is installed in a cylindrical recess in the end of the tension roll concentrically to the roll driving shaft that extends through the recess. The inside end of the spiral spring is attached to the shaft and the outside end is attached to the roll so that when the shaft rotates the tension roll is driven elastically by way of the spiral spring. The shaft for the tension roll and the other cooperating roll are provided with sprockets for being driven with a chain that is translated by sprockets on the shafts of the rolls and an electric motor. In this patent, the mechanism includes a lead screw operated with a chain and gear system to switch the take-up roll to becoming the unwind roll for the web and, vice versa, when the end of the web is reached.
Among the problems of driving the rolls of a sign module with chains and sprockets is that these components must be lubricated regularly to maintain good operation and inhibit corrosion. Applying lubricant to the components of a sign that is mounted on a tall structure is an inconvenient and unpleasant task. Dripping of lubricant which is commonplace with chains is another problem. Chains also have the undesirable characteristic of becoming less flexible when the ambient temperature drops to below zero degrees on the Fahrenheit scale, which is not uncommon during the winter in the northern states. A stiff chain reassures a greater force to bend it around the sprockets which can result in overloading the motor.
A loose chain may come off the sprockets and an excessively tight chain may impose a greater load on the small electric motor that drive a sign of this type.
U.S. Pat. No. 4,773,176, which was granted to Grehan on Sep. 27, 1988, also drives a tension roll in a sign module by way of a spiral spring. In this patented design, the tension roll has internal bearings for turning on a shaft which has an axial length that is greater than the axial length of the roll so one end of the shaft extends axially from the roll. The rolls in the module are driven with a flexible toothed belt running on toothed pulleys. A toothed pulley fits on the end of the tension roll shaft. The pulley has a large axial counterbore in which there is a spiral spring arranged concentrically to the shaft with the inside end of the spiral spring attached to the shaft and the outside end fastened to the toothed pulley. Hence, when the pulley rotates it causes an elastic or yieldable torsional force to be applied to the shaft so the shaft and roll can change their angular relationship to compensate for the overall change in the diameter of the roll and the web thereon that results from the amount of web on one roll decreasing while increasing on the other roll.
One problem that is inherent in modules driven with a toothed belt is that thermal expansion of a belt differs substantially from the thermal expansion of the metal frame that supports the components of the module. Hence, at low ambient temperatures, the toothed belt may become too loose and at high temperatures the belt may become too tight. An excessively tight belt can impose a large radial load on the motor and the bearings for the rolls and a loose belt can become unmeshed from the toothed pulleys. Moreover, in cold weather toothed belts become stiffer and require increased force to bend around the pulleys. This also imposes a greater load on the motor which could make the module inoperative under certain temperature conditions.
U.S. Pat. No. 3,255,541, which was granted to B. H. Bettcher on Jun. 14, 1966, discloses another version of a scroll module. In this patent a web tension maintaining roll has stub-axles extending axially inwardly by a short distance at opposite ends of the roll. The stub-axle at the driven end of the roll extends coaxially from a pinion gear that is driven by a motor driven gear train. A helical spring is mounted concentrically to the stub-axle. One end of the helical spring is attached to the driven stub-axle and the other end of the spring is attached to the roll to thereby provide an elastic connection between the power driven stub-axle and the roll to compensate for the changing overall diameter of the web on the roll as the web is transferred between the parallel arranged tension and cooperating rolls. The Bettcher patent module would have the problems incident to driving the rolls through a gear, sprocket and chain arrangement as has been explained.
U.S. Pat. No. 5,673,504 which was granted to Brown on Oct. 7, 1997, also discloses a module wherein a tension roll is driven elastically through the agency of a spiral spring. In this patented design a module is comprised of the usual laterally spaced apart frame members between which two web winding and unwinding rolls are positioned. To provide for rotation of the tension roll, bearing members are fixedly mounted in each of the spaced apart module frame members in coaxial relationship. The bearing members each have a central bore constituting an inside bearing or bushing for an axle and have a smooth concentric periphery constituting an outside bearing on which an end cap for the roll can rotate. The end cap contains an annular recess for containing a spiral spring that is positioned inside of the roll. A pulley for driving the roll rotationally with a belt is positioned outside of the frame member and a stub-axle that is unitary with the pulley extends axially from it for being journaled in the bushing and for extending into the spring recess in the end cap to provide for connecting the inside end of the spiral spring to the stub-axle and the outside end of the spring to the end cap. Since the end cap is latched to the roll, when the stub-axle is driven rotationally by means of the belt and pulley, a torsional force is applied to the end cap through the spring for rotating the tension roll. There is no simple way of providing for manual operating means in this patented design nor is backlash assuredly prohibited.
The module design first discussed has the disadvantages of being belt driven as previously explained. Moreover, the drive pulley for the tension roll and the pulley for the cooperating roll are outside of the module frame member so the modules must be undesirably spaced apart from each other by at least the width of a pulley when the modules are juxtaposed to compose a sign.
Additional patent references that disclose driving a tension roll in a module through the agency of a helical spring are U.S. Pat. No. 4,110,925 which was granted to Strand et al. on Sep. 5, 1978 and U.S. Pat. No. 1,902,884 which was granted to Wagner on Mar. 28, 1933.
The foregoing observations about preexisting scroll sign modules reveals that they are not optimized for trouble free operation. As explained, chain and belt drive systems are often adversely affected by changes in temperature wherein the chains or belts may stretch excessively, contract excessively, become stiff or too soft, or possibly drip oil as a result of requiring regular lubrication. It will be evident from inspection of the arrangement of the parts in pre-existing modules that differential expansion and contraction can occur that can prevent consistent module operation through a range of temperatures. Also, when timing belts and chain drive systems are used, an inventory of different sizes of belts or chains must be kept to cover changes in module sizes. Thus, according to prior practice, each module size requires individual parts that are not exchangeable between modules of different sizes. Pre-existing belt and chain drive systems also will have the inherent problem of allowing the web to relax, that is to lose tension, in the information display area between the tension roll and its cooperating roll due to backlash of such flexible drive systems.
Another limitation in pre-existing roll sign module drive systems is that they can be operated only with a motor and are without means for advancing the web in one direction or the other manually. In pre-existing designs, it is necessary, but not really practical, to grasp a chain or a belt and pull on it to translate it and thereby turn over the gear or sprocket system that is required for driving the web rolls rotationally.